Electromechanical control and indicating system



y 1954 c. e. ROPER. Re. 23,850

mc'mouEcumxcAL CONTROL AND INDICATING sYs'rEu Original Filed Oct. 21. 194'Z 8 Sheets-Sheet 1 uwmrox. Char/es (1. Roper Baht; +QJ

July 13, 1954 C. G. ROE'ER ELECTRONECHANICAL CONTROL AND INDICATING SYSTEM 8 Sheets-Sheet 2 Original Filed Oct. 21. 1947 mm mm 5 k m% C July 13, 1954 c. G. RQPER ELECTROIIECHANICAL CONTROL AND INDICATING SYSPEI Original Filed Oct. '21, 1947 8 Shegts-Sheet 3 INVENTOR.

I TL Char/es G. Roper July 13, 1954 3. G. ROPER 'R .8

'ELECTROMECHANICAL com-R01. AND mmca'rmc' SYSTEM Original Filed oer. 21. 1947 a Sheets-Sheet 4 I0 45 Fezoam I ir 69 K I 12 INVENTOR.

BY Char/es G. Roper fio q; 0 5ml:

3, 1954 c. s. ROPER Re. 23,850

ELECTROMECHANICAL CONTROL AND INDICATING SYSTEM Original Filed Oct. 21. 1947 8 Sheets-Sheet 5 Am phflzr D dvcfor wlfh SlnslrPnKLl INVENTOR- Charles G. Ropermgs.

y 1954 c. e. ROPER Re. 23,850

I ELECTROIIECHANICAL CONTROL AND INDICATING SYSTEM Original Filed Oct. 21, 1947 8 Sheets-Sheet 6 IN V EN TOR.

1 1 11 BY Char/as 6m Aff'gs.

y 1954 c. a. ROPER Re. 23,850

ELEC'iROMECHANICAL CONTROL AND INDICA'IING SYSTEM Original Filed Oct. 21. 1947 8 Sheets-Sheet 7 INVENTOR CHARLES G. ROPER BY EwfrQaJ ORNEYS 1954 c. a. ROPER Re. 23,850

ELECTRmlECHANiCAL CONTROL AND INDICATING SYSTEM Original Filed 001;. 21. 194'? 8 Sheets-Sheet 8 D.C. INPUT INVENTOR.

har/5 Q. Roper BY w fiaJ Reissued July 13, 1954 R 23,850

ELECTROMECHANICAL CONTROL AND INDICATING SYSTEM Charles G. Roper, Fairfield, Conn., assignor to Manning, Maxwell & Moore, Inc., New York, N. Y., a corporation of New Jersey Original No. 2,614,163, dated October 14, 1952, Serial No. 781,066, October 21, 1947. Application for reissue September 30, 1953, Serial No.

12 Claims. (Cl. 340-187) Matter enclosed in heavy brackets I: appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

1 This invention is concerned with various forms of electro-mechanical control and indicating systems for process control and indication of the magnitude of variable factors involved in such The many other and more detailed objects of this invention will be apparent from the following description of the several embodiments of the invention illustrated in the attached drawy tems- 7 ings as indicative of the scope of the invention An object of this invention is to provide elecherein disclosed. tro mechanical control and indicating systems of This invention resides substantially in the this type employing electro-mechanical degenercombination, construction, arrangement and ative operation to provide high gain stable direct relative location of parts as will be hereinafter current amplification for low impedance, low described. current inputs. In the accompanying drawings- Another object of this invention is to provide Figure 1 is a diagrammatic and schematic illusan electro-mechanical degenerative control and tration of a temperature controlled electro-meindicating system by means of which heat procchanical measuring System, in acc d ce w th esses may be automatically operated. this invention, comprising a stabilized direct Another object of this invention is to provide current amplifier; v such a system adapted to the indication of the Figure 2 is a diagrammatic illustration of the maximum of a plurality of related temperature essential elements of the system of Figure 1; conditions as well as to provide means for selec- Figure 3 is a top plan view of the senser unit tively determining the source of such maximum 2 of this invention in one practical form shown temperature. within a housing with the cover removed;

It is a more specific object within the scope Figure 4 is avertical, longitudinal, cross-secof the former objects to provide an automatic tional view taken on the line 4-4 of Figure 3; indicating system applicable, for example, to the Figure 5 is a detailed cross-sectional view with supervision of the operation of an internal comsome parts broken away taken on the line 5-5 bustion engine or engines whereby a continuous of Figure 4; indication of the temperatures of the bearings Figure 6 is a circuit diagram of a system emthereof, for example, is provided to the extent ploying the foregoing elements of this invention that the temperature of the hottest bearing of a for the purpose of indicating the maximum on a plurality is indicated. plurality of temperature conditions simultane- It is a still more specific object of the invenously monitored; tlon to provide in such a system selector means Figure '7 is a diagrammatic and schematic illuswhereby the hottest bearing can be located. tration of a form of the invention as employed It. is also an object of this invention to provide to control a heat pr electro-mechanical degenerative control systems Figure 8 is an expanded schematic illustration whereby processes may be automatically conof the electrical circuits of Figure 7; trolled in accordance with changes in a variable Figure 9 is a diagrammatic circuit illustration factor affecting the operation of such processes of the elements of the system of Figure 7; as, for example, temperature pressure conduc- Figure 10 is a diagrammatic and schematic tivity, liquid flow, and the like. illustration of another embodiment of the in- It is a general object of this invention to provention providing a remote null point indicating vide systems of the above types wherein the elec- (or controlling) system for measuring pressure trical portion thereof involves the use of vacuvariations; um tube Oscillators t attain Stable high gain Figure 11 is a circuit illustration of a system amplification for low impedance current input. lik that of Figure 6 to which has been added Another object of this invention is to provide means for selecting the source of highest tema system for control, indication, or both, wherein perature from a plurality of sources simultanevariations of an electrical or mechanical force ously monitored; are used to produce an amplified output by means Figure 12 is a diagrammatic and schematic 01' an electrically stabilized relay. 5 illustration of the application of the subject mat- 3 ter of this invention to a servo-ammeter or direct current indicator for indicating the magnitude of any variable which can be represented by a direct current; and

Figure 13 is a diagrammatic and schematic illustration of a modified system employing the senser unit to operate circuit contacts to regulate the magnitude of a current representative of a variable as distinguished from controlling the operation of an oscillator as in the previous systems.

The systems herein disclosed employ an electromechanical degenerative system to provide high gain, stable D. C. amplification for low impedance, low current inputs. There is illustrated herein not only systems of this kind but several embodiments of the possible applications thereof.

Some of the advantages of such a system can be emphasized by pointing out some of the disadvantages of prior methods of D. C. amplification. The wholly electronic tube D. C. amplifier is subject to drift resulting from supply voltage variation, tube characteristic in stability and the effects of temperature and humidity. Amplifiers of this type do not lend themselves to low impedance inputs. When voltage regulation and balanced circuits are used to reduce drift such amplifiers become complicated and unwieldy. For industrial and aircraft use, complexity and size not to mention cost are of vital importance and render such amplifiers of limited utility for such uses. The chopper type D. C. amplifier while it can be used with a low impedance input structurally is difficult and expensive to make. For many industrial purposes, as well as aircraft applications, where space and weight are at a premium, it is inconvenient and its extremely high gain is unnecessary.

The above difficulties are avoided by means of the basic combination of this invention. In that combination a low level voltage input to a galvanometer is converted into motion and this motion is then employed to tune an oscillator by means of the movement of a metal flag, or planer control element, to vary the output of a tuned grid-tuned plate oscillator. The motion of the metal flag loads and unloads the tank circuit of the oscillator with consequent variation in the input voltage of the oscillator. With a reasonably sensitive galvanometer movement, such means of operation can easily supply voltage gains of However, in accordance with this invention, the galvanometer is provided, for example, with an extra coil and the output voltage of a direct current amplifier fed by said oscillator, is applied to that extra coil. This extra coil measures the output current in relation to the input current by supplying a force which is applied in opposition to the original force of the input current. This provides a stabilized D. C. feedback amplifier system of considerable simplicity. As the input coil of the galvanometer comprises a relatively few turns of wire, the input impedance is low. The galvanometer is so constructed as to provide an extremely high gain mechanical input stage, eliminating the necessity for input tube selection and close control of operating conditions. The extremely high initial gain of such an electromechanical D. C. amplifier provides a large feedback factor, thereby reducing over-all drift of the amplifier with a resultant gain sufiiciently large for many control and indicating purposes.

An additional advantage 01 such a combination resides in the improved time respon e 01 the galvanometer. In other words, the natural undampened period of such a mechanical system is reduced to a fraction of its original value.

Another advantage of this system, when used as a voltage amplifying system, resides in the ability to completely compensate the input circuit for copper temperature error, thus eliminating necessity for heat insulating the input circuit and adding large zero temperature coefficient resistors, the use of which reduces the sensitivity of the system. This compensation results from an arrangement which causes the percentage change of current through the input coil of the galvanometer to be equal to the percentage change in the feedback coil. The loss of input sensitivity is balanced by decrease in the feedback factor and the gain remains constant with temperature changes. A system of this type may be operated with a current input in which case no temperature compensation is necessary.

In'one general classification of the systems herein disclosed the radio frequency oscillator output is rectified to provide a direct control and/or indicating current and a feedback current employed for output stabilization. In the other classification, the change in the D. C. impedance of the oscillator tube is employed to unbalance a bridge, and, thereby, provide the desired control and/or indication current and a feedback current employed for output stabilization.

It is important to note that in systems of either type frequency variation need not be considered, as only the magnitude of the radio frequency signal is significant, and thus frequency stabilization need not be provided.

In accordance with this invention in order to avoid the known weaknesses of a galvanometer, such as fragility and sensitiveness to acceleration and vibration, a special galvanometer design is provided, as part of this invention, resulting in a very rugged structure.

As a system of this type is effective for all desired purposes with a very small movement of the metal fiag with respect to the oscillator coils, the galvanometer or senser unit, herein disclosed, is entirely feasible.

Before describing the various circuit combinations, the galvanometer Ill hereof will be described in detail, with reference to Figures 3, 4 and 5. It is illustrated as comprising a suitable housing or container I having a removable cover 2. Within the compartment thus formed is a magnetic structure comprising a steel disc 4 closing the lower end of a cylindrical permanent magnet 3. The upper end of this magnet is closed by means of a steel plate 6 having a central aperture 9 into which the reduced end of the concentric iron core ll lies. The core is attached to the plate 4 by means of a machine screw H. The plates 4 and 6 and the magnet 3 are connected together by means of the screw 5 and threaded rods and nuts I and spacers I. Forming part of this unit is a supporting plate I! forming a cantilever extension. This structure provides a magnetic field of cylindrical formation and of uniform fiux distribution.

Mounted upon the plate I! by means of the screws I4 is a supporting bar 13 to .which is attached by means of the screws l6, a clamping plate is. A light rigid bar l1, having a pair of transverse extensions II, is supported by the clamping action of the clamp bar IS on these extensions, which lie between it and the bar II,

as shown in Figures 4 and 5. A light lever is is provided, intermediate its ends, with a pair of upstruck tabs 20. These tabs are riveted to the arm II. The result is that the lever I9 is resiliently supported by means of the flexible extensions IB of the arm IT. The extensions l8 provide leaf springs, preferably made of thin ilexible metal which act as cantilever or flexure bearings by means of which the lever i9 is supported. They provide for adequate angular motion of the lever l9, while maintaining positive stability transversely of its length. This resilient support for lever I3 is to be distinguished from the usual pivotal support for the pointer of a D'Arsonval galvanometer comprising a shaft joumaled in bearings. A coil form 2| is attached to the end of the lever l9 which overlies the core 3. Wound, on the coil form are a pair of insulated copper coils, which are diagrammatically illustrated in the various figures as, for example, in Figures 1 and 2, as the coils 3B and 39. Thus, it will be seen that these coils aresuspended in the cylindrical magnetic field of the permanent magnet, and their movement with respect thereto is at right angles to the magnetic field, insuring maximum electrical reaction upon movement of the coils in that field.

Suspended from the plate I2 is a bracket 22 provided to support the lower end of a coil spring 23, the other end of which is attached to the lever I! to preload it.

An insulating support 25, attached to the plate 12, has mounted thereon any suitable form of terminal clips arranged in the pairs 26 and- 21. Light flexible leads 28 and 29 extend from the coils 38 and 39 on the coil form 2! to these terminal pairs, as illustrated in Figure 3. It will be understood that these lead pairs may be of such light construction as to in no way interfere with the movements of the lever or beam IS. A longitudinally positionable screw and nut 24 is mounted on the beam I! to provide means for adjusting roughly the balance of the beam. Fine adjustment is provided by sliding the small weight 24' along the edge of the beam.

Supported on the plate i2 near its right hand end by means of three adjustable screws 34, is a housing 30 in which are mounted in spaced parallel relation the oscillator coils and 33. This housing is mounted on the plate I2 by means of the screws 3|, engaging threads in the screws 34, and by adjustment of the screws 34 coils 32 and 33 can exactly be positioned, with respect to the right hand end of the beam [9 forming the metal flag or planar control element, previously referred to.

Journaled in the housing I is a shaft 35 which is attached to the inner end of a spiral bi-metallic coil 36 producing automatic cold-junction compensation. The outer peripheral end of this spring is connected by a rigid connection 31 to the outer end of a spiral hair spring H attached at the center to the end of the light arm By means of a friction device of any suitable kind such as the loading spring 35" on shaft 35 hearing on the loose collar 35' attached to the housing I, a desired friction maintains any preload applied to the beam through the spring H. A pointer such as the pointer 38 of Figure 1 may be attached to the manual on shaft 35 for rotation with it.

The senser unit of Figures 3, 4 and is more diagrammatically illustrated in Figures 1 and 2. A simpler form of the system, in accordance with this invention. is illustrated in these latter figures. As illustrated, the coil 36 is the input coil and is shown connected to a temperature sensitive device such as a thermocouple 40 which will generate an electrical current proportional to temperature changes. Of course, in the the actual galvanometer the thermocouple leads will be connected to the terminals 26. Figure 3. Considerlng Figures 1 and 2 together the oscillator coils 32 and 33 form part of a tuned grid-tuned plate vacuum tube oscillator 46, of a well known type. In order to prevent the introduction of an error due to stray fields, static charges and the like, the common point of these coils is preferably grounded as indicated at 41. One of these coils, as for example coil 32, is shunted by a small variable capacitor 52 to aid in initial adjustment of the galvanometer.

The power supply for the apparatus is provided through the leads 42 to a suitable trans former full-wave vacuum tube rectifier and filter circuit 48, likewise of well known construction. a

The usual adjuncts of the oscillator include the large condensers 56 and Si for blocking the flow of direct currents in the radio frequency circuit, and the use of a radio frequency choke coil 49 for blocking the flow of alternating currents from the output circuit of the oscillator. The resistor 53 provides a grid bias for the oscillator cathode and the oscillator, as illustrated, employs a tetrode in which the screen grid is directly connected to the plate. Capacitor 5| also forms part of the grid lead circuit which includes resistor 53, so that with increasing amplitude the control grid is more negatively biased. In the output circuit of the oscillator are resistors R1, R2, R3 and R5 to which one of the feedback leads 43 is adjustably connected, as shown, through a suitable voltage proportioning resistor R4. The other lead for the feedback coil 33 is connected to the grounded cathode, as shown. The direct current output circuit is provided by the leads 45, one of which is grounded and the other of which is connected to the variable tap for the resistor R2.

As illustrated in Figure 1, an indicating device 44 may be provided by means of which, upon suitable calibration, variations in the temperature being measured can be indicated. As will appear later, the output circuit 45 may also be employed either with or without indication to effect control of a process the temperature of which is being monitored by the thermocouple 44. To complete the explanation of the relationship of Figures 1 and 2, it is noted that the oscillator-amplifier mechanism has been generally indicated by the reference numeral 4|. As previously mentioned, the shaft 35, see Figure 1, may be provided with a pointer 38' operating on a scale to mechanically indicate upon proper calibration the temperature changes; being measured or monitored.

A study of Figure 2 will indicate that the oscillator feeds an adjustable direct current bridge with the tube 46 in one leg, providing a high load resistance. It will be readily understood that as the temperature changes the thermocouple current will vary in the coil 36, effecting a movement of the beam I9 and, therefore, the flag end thereof, with respect to the coils 32 and 33. This movement of the flag will provide a change in load on the tank circuits of the oscillator with consequent variation in the output voltage of the oscillator. As a result the resistance of oscillator tube in one leg.

of the bridge will vary, in accordance with changes in the temperature of the source bein monitored by the thermocouple 40. It follows that this variation will appear as a voltage change in the output circuit 45, and effect a corresponding operation of the indicating device 44. mined by the resistor R; will be applied to the feedback coil 39 to partially balance or oppose the movement of the beam 19, which initiated these electrical variations.

To compensate for variations of input coil resistance with ambient temperature changes when a voltage input is being measured, a resistor Ra is connected in series with the input coil 38 and a resistor Rb is connected in parallel with the feedback coil 39. Rb are of the type which have azero temperature coefficient, of resistance. By selecting suitable values for resistors Ra and Rb any change in the current in input coil 38, resulting from a change in the electrical resistance of the coil, is compensated by an equivalent change of current in the feedback coil 39. Complete compensation is approached as the ratio of Ra to Rb becomes equal to the ratio of input coil resistance" to feedback coil resistance. This compensating feature can be used in the various systems herein disclosed.

All of the advantages of the general combination hereinbefore set forth result from this arrangement, one of the more important of which is the overall stabilization of the system resulting from the feeding back of a portion of the output current to the stabilizing coil 39 of the galvanometer.

This arrangement is very sensitive due to the large gain factor resulting from mechanical and electrical amplification of what may be very small mechanical movements of the metal fiag. Sensitivity is enhanced by the fact that all of the turns of the coils 38 and 39 cut across the lines of the magnetic field at right angles, and the low frictional-loss in the leaf spring supports for the beam. Mounting the coils at the end of the beam l9 provides a torque to input ratio that is higher than that usually attainable, which would be detrimental were it not for the feedback control provided. Additionally, the natural period of the system tends to be reduced by feedback, as will be apparent.

In view of the foregoing, it will be seen that this system combines the advantages of a high torque to current input ratio, rugged shock resistant construction, simplicity of assembly and a fast time response, all due to the feedback factor. In addition, the galvanometer construction is suitable as the input stage of a high gain stable D. C. amplifier. It will be understood, of course, that under some conditions additional stages of electrical amplification may be used so that very high overall gain ratios, as high as 50,000, can be provided, with stability.

This system also provides, by reason of the use of the high frequency oscillator, which simplifies rectification and filtering of the output, an impedance change from the low input impedance of the galvanometer coil 38 to the high impedance direct current output circuit. Feedback also accomplishes improved frequency response, and the high impedance output makes possible the addition, when required, of further stages of electronic amplification, all of which can be stabilized statically by feeding back from the final output circuit. This system also eliminates the necessity for voltage regulators of any A proportion of this voltage, deter Resistors Ra and sort and reduces the effect of disturbance, such as ambient temperature and humidity changes.

The use of the beam structure in the senser to provide mechanical measurement makes it possibleeasily to provide mechanical setting of the input operating level represented, for example, by adjustment of the tension provided by spring 23. Any steady component of input can thus be easily balanced out either by manual or automatic compensation.

The high impedance output plus the feedback feature of this system permits the output of several galvanometer or senser units I0 to be connected in parallel with the feedback coils of I the galvanometer in series, for selective amplification of the highest of a group of input signals. The system of Figure 6 is illustrative.

The system of Figure 6 may be employed to indicate the temperature of the hottest of a plurality of heat sources such as for example, the bearings of one or more aircraft engines. One disadvantage of present systems for this purpose is the necessity of providing a plurality of indicating instruments one for each of the bearings being monitored, a disadvantage in view of the already overcrowded instrument panels of the modern airplane. The system of Figure 6 provides a practical substitute employing only one indicating instrument. This system employs a plurality of combinations like that of Figures 1 and 2, and, therefore, similar reference numerals will be used wherever possible. The four senser units of Figure 6 are diagrammatically illustrated at 10. The midpoint of each of the pairs of oscillator coils 32 and 33 is grounded as before at 41. The operating coil 30 of each unit It! is energized by means of a thermocouple 40, one of each of which is associated with the bearing being monitored. The oscillator coils 32 and 33 form part of the tuned grid-tuned plate oscillators ll. The output circuit of each oscillator includes the radio frequency choke coil 49. The plate of each oscillator is shunted to ground through a radio frequency bypass condenser 58 and a half-wave rectifier 59 poled so that the positive pulses of the output current may return to the cathode. The common point of the condensers 58 and rectifiers 59 are connected to a half-wave rectifier 60 poled to pass the negative components of the output current to the grid of the common amplifier tube 62. All of the rectifiers 60 are connected in parallel to the grid of this tube. As before, the indicating meter 44 is in the output circuit of this final amplifier 62, and a desired portion of the output current as determined by the resistor R4, is passed in series through each of the feedback coils 3B of the senser units l0.

As circuit technicians will appreciate, when this circuit is in operation the thermocouple temperatures are measured by each of the senser units or galvanometers l0 and the levers or beams l9 thereof are each displaced in proportion to the magnitude of the thermocouple current of the associated thermocouple. Thus, the output of each oscillator ll will be proportionately varied. The positive half of each of the output currents will flow in the output circuits of the associated oscillators, and the negative halves of these currents will pass through the rectifiers 60 and negatively polarize the grid of the amplifier 62. Thus, the negative grid bias of this amplifier will be determined by the maximum negative voltage output of the rectifier 60, of the four rectiflers in parallel, connected to the oscillator associated with the thermocouple of the hottest bearing. Thus, the indicating lever 44, if properly cahbrated, will indicate the temperature of the hottest bearing monitored by this system. Although the system of Figure 6 will not indicate which is the hottest hearing, it will indicate whether one of the bearings being monitored has reached a dangerous temperature, so suitable precautionary measures can be taken. For many installations, it is obvious that it is more important to know when one bearing is dangerously hot rather than which bearing is overheated. The accuracy of this system is assured by feeding back the output current or a portion thereof, to the senser units in series and, suitable automatic bi-metallic compensation for cold Junction variation is provided as is illustrated in Figures 3 and 5.

It is convenient at this point to refer to Figure II which illustrates an amplification of the system of Figure 6 wherein the hottest bearing can be selectively determined. The system of Figure 11 is quite similar to that of Figure 6, and is illustrated as suitable for monitoring the temperature of four sources, as in the former case. In each of the leads from the thermocouples "is connected in series, a resistor 56, and means is provided for applying a direct current voltage successively across the' terminals of these resistors, either in aid of the voltage of the circuit or in opposition thereto.

The galvanometer or senser units It, the oscillators 4| and the amplifiers and rectifiers 4| are all shown connected in parallel to a common amplifier 52, the output of which is indicated by the meter 44. It will be understood that the combined amplifiers and rectifiers 4| correspond to the arrangement in Figure 6, whereby the amplifier 52 is fed with a-negative biasing potential comprising the amplified output of the amplifiers. It will also be understood that the feedback feature is also included in this setup. The supply leads 42 for the amplifier, in the event that a .D. C. source is employed, are also used to supply the test voltage through the reversing switch 54. Of course, the source of the test voltage can be different than the source for the amplifier, but the diagrammatic illustration in Figure 3 is suitable for the purpose of explaining the invention. The reversing switch 54 is connected to the movable contact of each of a pair of single pole four contact switches; the movable contacts of which are moved in synchronism by means of the manual on the shaft to which the movable contacts are connected. Each of the fixed contacts of the two sets of switches 55 are respectively connected to opposite sides of each of the resistors 55 as is clear from the drawing.

In the use of this arrangement with the movable contacts of switch 55 out of engagement with any of the fixed contacts, the system will wonk in the same manner as the system of Figure 6 indicating the highest of the four temperatures being monitored. By means of the switch 55 it is possible to determine whether all of the individual monitoring circuits are operating, and which particular one is monitoring the hottest bearing, in the case of a bearing testing system. By rotating the shaft of switch 55, it will be seen that the voltage from the circuit 42' can be successively impressed across the resistors G in the various thermocouple circuits. If the reversing switch 54 is in a position so that the test voltage is aiding the thermocouple 10 voltage, the reading onthe meter 44 for each thermocouple will be increased the same amount. Thus it will be seen that if an indication is given for each position of switch 55 it will be known that each monitoring circuit is operative. Likewise, the highest reading for all four positions of switch 55 will immediately indicate which thermocouple is reading the highest temperature since, of course, the fixed contacts of switch 55 will bear a known relationship to the thermocouples. In the event that the thermocouple indications are quite low, it is possible by throwa heat process at a predetermined controlled operating temperature. The system is very diagrammatically illustrated in Figure '7 employing the galvanometer III, as before, for controlling the output of an oscillator feeding a D. C. bridge,

as before, and employing the feedback feature. These elements are diagrammaticallyillustrated at 63 and include additional elements to be described. The final output of the circuit is an alternating current supplying a reversible induction motor 86, through the circuit connection 65 to in turn operate a valve 61 in the line 58, through which the heating medium passes to the process. The thermocouple 40, of course, meters the temperature of the process, and the apparatus is designed to correct any deviations in the temperature of the process from the predetermined value, by increasing or decreasing the supply of heating medium thereto.

The full mechanism of Figure 7 is shown diagrammatically in greater detail in Figure 8. The galvanometer or senser unit Ill is supplied through the input circuit by means of the thermocouple and controls the output of the oscillator 4| which feeds the high impedance D. C. bridge 69. A stabilizing direct current is fed back through the circuit 45 to the galvanometer as before. The fluctuations in D. C. potential across the'bridge 89 are fed into a stabilizing network III, which is designed to respond to the rate of change in magnitude of the frequency. The D. C. output (positive or negative) of the bridge 10 is applied to a phase control tube or stage -'II by *means of which the phase of an alternating current of lower frequency is reversed and fed to the input of a push-pull amplifier II. This amplifier increases the amplitude of the low frequency current to a value suitable to operate a reversible motor 66 which drives the valve 81. A power rectifier 14 supplied through the circuit 13 provides the D. C. operating potentials for the various circuit subcombinations.

The system diagrammatically illustrated in Figure 7 is shown in sufiicient detail in Figure 9 to permit reproduction by those skilled in the art. It will be seen that up to the stabilizing network ill the circuit is the same as that illustrated in Figure 2 and similar reference characters have been 'employed. The only change which does not involve a difference is that the resistors R1, R2 and 'Rs have been combined into resistor R2. The direct current output of the bridge 89 supplies positive and negative signals through the stabilizing network 10 to cause cortriode of the phase control stage II.

responding polarization of the grids of the duo- A pulsating direct current flows in the output circuit due to A. C. energization, as shown, of a magnitude proportional to the magnitude and rate of change of the signal from the bridge 88. The pulsating direct current flowing in the primary of the transformer produces an alternating current in the secondary thereof which is amplifled by the second duo-triode by the push-pull amplifier 12 to supply an alternating current suitable to operate the motor 88 in either direction, depending upon the direction of deviation of the temperature of the process being monitored from the predetermined setting.

Circuit technicians will understand that when the temperature being monitored is constant, and at the preselected value, there will be no change in current flowing in the D. C. bridge 88. Hence, the phase control stage Ii will be in balance. It follows, therefore, that the motor 88 is at a standstill. Should the temperature drop from the predetermined value an alternating current of proper phase will appear in the output circuit of the push-pull amplifier 12 to energize motor 86 to operate the valve 61 to supply more heating medium to the process. As the temperature returns to the preselected value, the energizing current for motor 88 will die out. On the other hand, if the temperature of the process being monitored rises, motor il-will be operated in the reverse direction to close valve 81 and cut off the supply of heating medium.

Upon review it will be seen that this system is adapted to rectify the high frequency oscillator output to provide a direct current for feedback purposes and controls the operating current for motor 86.

Figure diagrammatically illustrates a system for remotely indicating changes in a variable such as, for example, pressure changes. In this arrangement the transmitter T includes the galvanometer 18, which is similar to that previously described, with the exception that the coil 88 has been dispensed with, leaving only the feedback coil 88. The oscillatable beam I8 is used as before with one end interposed between the oscillator coils 82 and 88, forming part of the vacuum tube oscillator 18. The pressure fluid is supplied through the line 18 to a Bourdon tube 15, which is connected by means of a resilient link 11 to the beam l8. The purpose of link 11 is to convert the motion of the Bourdon tube 18 into an operating force for the beam l8. Coil 88 is connected in the output circuit of the oscillator, as before, and to any suitable form of detector unit 88, which can be a vacuum tube detector. The remote indicating system is shown generally at I and includes another galvanometer [8 just like that at the transmitting end. The beam i8 of this galvanometer has its flag end related to the oscillator coils 82 and 88 forming part of the oscillator 18. The output of this oscillator is connected to the coil 88 of the calvanometer and, also, to the input of the detector 88. The output of the detector is fed to an amplifier 8i which may be a system such as that shown in Figure 9, wherein the output of the amplifier comprises an A. C. current to operate the servomotor 82. This servomotor is connected by a friction drive wheel or pinion 88 with a driven gear or friction wheel 84 in the form of a graduated dial. The dial is, of course, rotatably mounted, and is connected by means of a spring 88 to the beam l8. A fixed pointer 88 oo- 12 operates with the graduations on dial 88 to in dicate the magnitude of the pressure being measured.

In the operation of this system, pressure changes in the line 18 will cause a movement of the free end of the Bourdon spring 15, which movement will be transmitted through the link 11 to the resiliently mounted beam -l8. The flag end of the beam will move with respect to the oscillator coils 82 and 83 and, thereby, change the amplitude of output of the oscillator in a direction corresponding to an increase or decrease in pressure in the line 18. As a result, the output current will flow to ground through resistor 18', producing a voltage proportional to the pressure. The current flowing in coil 88 balance the force of spring 11. For any position of the disc 84 aforce is .applied to the beam [8 through the spring 88. Thus, the beam l8 will be tipped in the proper direction to cause the oscillator 18 to have its output varied in the proper direction. The output of this oscillator is fed to the coil 88 of the indicating galvanometer l8 and, also, to ground through resistor iii. If the voltage drop through resistor lfl does not equal the voltage drop through resistor i8, current will flow through the detector 88 to the con trol output of amplifier 8| and hence the operating current for motor 82, operating it in the proper direction to apply a force to the beam i8 through spring 88 to vary the output of the oscillator 18 until the voltage drop across [8 equals that across ill". The system is then in null balance and the magnitude of the pressure being measured is indicated on dial 88. At this point it will be noted that the magnetic reaction of the coils 38 will be in a direction to oppose the movement applied to the beam IQ of each galvanometer. Thus, upon proper calibration of the dial 84, its relative position with respect to the pointer 85 will indicate the pressure in the line 18. This system provides a method of converting pressure variations into calibrated indications of the value thereof at a remote point, and these indications will be proportional to the potentials which are in null balance.

It will, of course, be understood that other variables, including potentials, can be measured by properly changing the actuator for the transmitting galvanometer beam. For example, temperature charges could be employed to mechanically, as well as electrically, affect the position of the transmitting beam I8 to produce similar operations.

The system of Figure 12 is a modified arrangement for indicating the variations in the magnltude of variables, whose variations can be converted into direct current. As in all previous cases, the galvanometer I8 is employed, but which in this case has only the input coil 88, the feedback coil having been eliminated. The D. C.

.input circuit to this coil is supplied with the varying direct current, which is representative of the variable factor to be measured. The resiliently mounted beam [8 is supported in this case by means of a bar 81, and as in the previous cases, the arm i8 is connected to the beam for angular movement therewith. At 88 is a shaft rotatably supported in bearings, not shown, and connected to the end of the lever I! by means of calibrated spring 88. The shaft is also connected 3% the support 81 by means of a return spring pointer 82. The pointer moves over a suitably calibrated dial 8!. A motor 84 drives the gear Secured to the shaft is a gear 8| and a cacao 9i. The flag end of the beam I9 is displaceable with respect to the oscillator coil 98, forming part of a combined oscillator and full wave rectifier 95. The power supply is from the line 91. The oscillator and rectifier functions are performed by the combination triode and diode, the triode providing one-half of the full wave rectifier, which includes the diode.

The direct current input, varying in proportion to changes in the variable to be measured, is fed to the coil 39. The reaction of this coil on the magnetic field of the galvanometer causes a displacement of the beam I9 and, of course, its flag end, with respect to the oscillator coil 98. This movement of the fiag result in a change in the output of the oscillator 95, which output is fully rectified toprovide an A. C. operating current for the motor 94. Of course, the displacement of the beam I9 stresses the calibrated spring 89. Operation of the motor 98 causes the shaft 88 to revolve with the result that the pointer 98 is proportionately displaced on the dial 93 to indicate the value ofthe variable being measured. The output of the oscillator will be proportional to the displacement of the beam and, therefore, motor 98 will operate the pointer 92 until the springs 89 and 98 are stressed to a point to balance the drive force of the motor..- The pointer thereupon comes to rest, and remains stationary until the variable D. C. input varies, either by increasing or decreasing. If it increases the pointer will be moved further up the scale, and if it decreases the output of the oscillator will decrease reducing the torque on the motor 94, which is then driven down scale to a balanced condition by the return spring 98. Thus, the pointer moves down the scale to indicate the new value of the variable. The pointer comes to rest on the up scale movement of the pointer by reason of the balancing force of the calibrated spring 89, acting through lever I! on the beam I9 to balance the magnetic force of the galvanometer produced by the direct input.

There is disclosed in Figure 13 in a schematic and diagrammatic manner, a further application of the principles of this invention wherein the galvanometer or senser unit is employed to produce an amplified direct current voltage proportional to variations from a current the magnitude of which is representative of the fluctuations of a variable. In this arrangement the senser unit l8 again employs both the coils 38 and 39 mounted on the resiliently and pivotally mounted beam I9 as in previous cases. The D. C. input to be magnified is applied to the coil 38 through the leads marked D. C. input, from any source of pulsating direct current such as a thermocouple.

Connected to the beam I9 for oscillation therewith is the arm II as before, which is connected by means of a spring 36 to a shaft carrying a pointer 38 operable with respect to a fixed scale.

' of variation input current. Mounted on the in sulated bracket 99 is a fixed contact positioned to cooperate with a contact I88 mounted on the beam I9 and in electrical contact therewith. The fixed contact is connected by a wire to a suitable source of direct current 98. The movable contact I88 is grounded as shown. The other side of the current source 98 is connected to one terminal of each of the resistors I82 and I88 by means of the wire l8I. Resistor I88 is provided with a movable contact connected to wire I89 which connects to .one terminal of coil 39, the other terminal of which is grounded at II8, as shown. The other terminal of resistor I8! is connected to one terminal of resistor I88, the common terminal of which is connected to ground through a capacitor I83. One of the output leads I81 is connected to the other terminal of the resistor I84 which is grounded through capacitor I85. The other lead I81 is grounded and a resistor I88 is shunted thereacross.

The operation of this system is in the nature of a voltage regulator by means of which a small measuring voltage actuates the device to regulate the supply of voltage from the high potential source 98 so that an amplified D. C. voltage appears at the output terminals I81. In view of the previous disclosure it will be appreciated that when a direct current is supplied to the coil 38 beam I9 is rotated on its supports causing movable contact I88 to engage the fixed contact. As a result the battery 98 will apply its potential instantaneously to the circuit of resistor I88 and coil 89, causing current to how and producing a magnetic force in opposition to the force of current in coil 88. Thereupon, beam 39 reverses its rotation and movable contact I88 disengages the fixed contact, stopping the flow of, current in coil 39. This operation will then repeat to give beam I9 an oscillating motion and produces a pulsating direct current in the circuit of resistor I88 and coil 39. 'The pulsating direct current applie a voltage to the circuit of resistor I86 which is proportional to the average value of the current and the resistance in the circuit of coil 39 and resistor I88. The values of the resistors I82 and I84 and capacitors I83 and I85 are selected to reduce the pulsating component of the applied voltage to required values. Since the average value of the current in coil 39 is proportional to the current in coil 38, the output voltage at I81 is proportional to the D. C. input to coil 38.

Thus it willbe seen that the galvanometer or senser unit herein disclosed may be used for control, and if desired indicating functions, without employing an oscillator in combination therewith.

In view of the wide variation in the application of the principles of this invention as indicated by this disclosure, it will be apparent to those skilled in the art that the subject matter of this invention can be embodied in many physical forms, and I do not, therefore, desire to be limited except as required by the appended claims.

What is claimed is:

1. In a continuous control system the combination comprising a galvanometer having means forming a magnetic field, a resiliently mounted member, and an input coil, said coil being connected to said member and mounted in said magnetic field. a vacuum tube oscillator having a tank circuit, the movement of said member varying the load of said tank circuit to produce an amplified direct current, electrical means, energized by said direct current, acting to oppose the displacement of said resiliently mounted member, means connecting to said input coil for generating a current proportional to the deviation of a condition to be controlled from a predetermined value, and means actuated by said direct current for causing said condition to return to its predetermined value.

2. In the combination of claim 1, means for 15 resiliently loading said member to preselect said predetermined value.

3. In a control system the combination comprising a galvanometer having means forming a magnetic field, a pivoted beam, an input coil and a stabilizing coil connected to said beam and mounted in said magnetic field, a vacuum tube oscillator having a tank circuit, the movements of said beam varying the loading of said tank circuit to produce an amplified direct current, said stabilizing coil being energized by said direct current, means connected to said input coil for generating a current proportional to the deviation of a condition to be controlled from a predetermined value, and means actuated by said direct current for causing said condition to return to its predetermined value.

4. In the combination of claim 3, means for resiliently loading said beam to preselect said predetermined value;

5. A metering system 01' the type described comprising in combination a pivoted metallic beam having input and feedback coils fixed thereon. means for producing a fixed magnetic field in which said coils move along the axis of said field, means for energizing said input coil to effect displacement of said beam, and means for supplying a direct current to said feedback coil in response to displacement of said beam including an oscillator having an input and an output circuit and a tuning coil in at least one of said circuits positioned adjacent one end of said beam, said feedback coil opposing displacement of said beam.

6. In the combination of claim 5, means for compensating for the effects of ambient temperature variations on the resistance of said input coil and said feedback coil comprising resistors of zero temperature coefiicient. one in series with said input coil and the other in parallel with said feedback coil.

'7. A metering systemv of the type described comprising in combination a vacuum tube oscillator having a tunable tank circuit, a galvanometer having an operating coil, a signal input circuit for said coil, a resiliently mounted member proportionally displaced by energization of said coil, said member being displaced with respect to said tank circuit to vary the output of said oscillator upon movement of saidmember, an output circuit for said oscillator in which the voltage is proportional to the displacement of said member, a second coil energized by said oscillator for opposing the displacement of said member, a work circuit connected to said output circuit, and means for compensating for the efiects of ambient temperature variation on the resistance of the operating coil and the second coil comprising resistors oi zero temperature coefiicient one connected in series with said operating coil and the other in parallel with said second coil.

8. A galvanometer of the type described comprising means forming an annular magnetic field, a resiliently mounted beam, a pair of coils secured to one end of said beam and disposed in said magnetic field, at least one inductance mounted adjacent an end of said beam, and spring means for preloading said beam.

9. In the combination of claim 8, said spring means comprising a rotatably mounted shaft and a spring for interconnecting said shaft with said beam.

10. A measuring device of the galvanometer type, comprising a displaceable member including a planar control element, means defining a magnetic field, a coil carried by said member and positioned within said field, mounting means for supporting said member at two points spaced apart such that the center of mass of said member is located between said spaced points, said mounting means including a thin resilient element positioned edgewise relative to the plane of said control element, thereby to permit limited'substantially frictionless angular displacement of said member by deflecting said resilient element against the resilience thereof, said angular displacement of said member producing movement of said control element in a. direction substantially perpendicular to the plane thereof, a planar inductance positioned adjacent said control clement, movement of said control element in said direction producing a substantial variation in said inductance and movement of said control element in a direction parallel to the plane thereof producing substantially' no variation in said inductance. whereby vibrations in said last named direction which are produced between'said control element and said inductance produce substantially no variation in said inductance, and means including a second resilient element for preloading said member.

11. A measuring device of the variable impedance output tyre, comprising a displaceable member including a planar control element, mounting means for supporting said member at two points spaced apart such that the center of mass of said member is located between said spaced points, said mounting means including a thin resilient element positioned edgewise relative to the plane of said control element, thereby to permit limited substantially frictionless angular displacement of said member by deflecting said resilient element against the resilience thereof, said angular displacement of said member producing movement of said control element in a direction substantially perpendicular to the plane thereof, a control impedance so positioned adjacent said control element that movement of said control element in said direction causes a substantial variation of said control impedance and movement of said control element in a direction parallel to the plane thereof causes substantially no variation of said control impedance, whereby vibrations in said last named direction which are produced between said control element and said control impedance cause substantially no variation of said control impedance, and means including a second resilient element for preloading said member.

12. A measuring device of the variable impedance output types, comprising a displaceable member including a planar control element, mounting means including a thin resilient element positioned edgewise relative to the plane of said control element for supporting said member to permit limited substantially frictionless angular displacement of said member by deflecting said resilient element against the resilience thereof, said angular displacement of said member producing movement of said control element in a direction substantially perpendicular to the plane thereof, a control impedance so positioned adjacent said control element that movement of said control element in said direc-' tion caused a substantial variation of said control impedance andmovement of said control element in a direction parallel to the plane thereof causes substantially no variation of said control impedance, whereby vibrations in said last named direction which are produced between said control element and said control impedance cause 17 18 substantially no variation of said control im- Number Name Date pedance, and means including a second resilient 2,234,184 MacLaren, Jr Mar. 11, 1941 element for meloading said member. 2,325,232 Davis July 27, 1943 2,362,562 Kelly Nov. 14, 1944 References Cited in the file of this patent 5 2,37 ,527 w n May 2 19 5 or the Original Patent 2,409,073 Sias Oct. a, 1946 UNITED STATES PA'I'EN'IS g i 13:;

r a \1 y Number Name Date 2,446,390 Rath Aug. 3, 1948 1,639,365 Brown Aug. 16, 1927 10 2,016,894 Faus Oct. 8, 1935 FOREIGN PATENTS 2,085,128 Staege June 2 1937 Number Country Date 2,117,894 Lenehan May 1938 179,805 Switzerland Dec. 2, 1935 2,154,260 Brandenburger Apr. 11, 1939 

